With the recent popularization of mobile communication terminals, there is need for using multiple telephone numbers depending on purpose. In order to meet this need, a user conventionally carried mobile communication terminals as many as telephone numbers he desired to use. However, since carrying around multiple mobile communication terminals is very inconvenient for the user, it has been proposed to make multiple telephone numbers available for one mobile communication terminal (see Patent Documents 1, 2, and 3, for example).
In addition, it has also been proposed to share a telephone number such as an extension number or the like with multiple telephones (see Patent Document 4, for example).